it's fine, u need to bring ur i-797 with you

it's fine to have a visa on ur passport with one employer and carry ur new I-797 h1b approval from another employer. As along as ur visa has not expired, u r fine and can enter US without any problem. U just need to bring ur i-797 with you, the airport immigration officer will ask u if u still with the same employer or not, u need to tell him/her and present the new 1-797.
I did the same and travel overseas several times without any problem.